Methanation activity measuring instrument

ABSTRACT

The present invention provides a specific methanogenic activity measuring apparatus, in which a carbon dioxide gas absorbing container  6  is removably accommodated in a pressure vessel  4  with a cover  3  removably set thereon, the pressure vessel  4  is removably accommodated in a thermostatic water bath  7  with a pressure transducer  8  based on the pressure-electricity converting system connected to a recorder  5  attached to the cover  3,  and further a supporting member for supporting a carbon dioxide gas absorbing container and a generated gas piping  16  are attached to an external bottom surface and an internal bottom surface of the carbon dioxide gas absorbing container  6  respectively, and gas piping  12  with valves for gas phase replacement to the cover  3  of the pressure vessel  4.

FIELD OF THE INVENTION

The present invention relates to a measuring apparatus for measuringspecific methanogenic activity of granular sludge used in an anaerobicwastewater processing method.

BACKGROUND TECHNOLOGY

As a known measuring apparatus for measuring specific methanogenicactivity of sludge, there is that used in a method called as “the vesselmethod” as disclosed in the publication “Journal of water and Waste (inJapanese) Vol. 37, No. 7 (1995)”, which is as shown in FIG. 12 and FIG.13, and description is made hereinafter for the apparatus. A pluralityof narrow-mouthed bottles 62, to each of which a gas conduit piping 61is disconnectably connected, are placed in water in a thermostatic bath63 with a stirring member 66 and a heater 67 installed in thethermostatic bath 63, a tip of the gas conduit piping 61 is inserted ina washing gas bottle 68 filled with 1N, NaOH, this washing gas bottle 68and a gas holder 69 are connected to each other with the gas conduitpiping 61, and a scale 72 is attached to the gas holder 69.

An operating sequence when measuring specific methanogenic activity ofsludge with the apparatus as described above is shown in an operationflow chart in FIG. 13, and in this flow chart,

(1) A first sludge to be measured is sampled,

(2) the sampled sludge and a reaction mixture are put in thenarrow-mouthed bottle 62 placed in the thermostatic bath 63, and is keptin the state for raising the anaerobic characteristics of the apparatuswith the stirring member 66 and heater 67 being operated for 12 hours at35° C.,

(3) A gas generated in the narrow-mouthed bottle 62 is guided throughthe gas conduit piping 61 into the washing gas bottle 68 filled with 1N,NaOH to remove CO₂, and then

(4) the gas is kept for 6 to 8 hours in the gas holder 69, and duringthis period up and down movement of the gas holder 69 is visually readwith the scale 72 once for every 1 hour to determine specificmethanogenic activity (slope) [gCOD], and finally

(5) gVSS of the sludge is measured for 24 hours.

Then based on the specific methanogenic activity (slope) and a quantityof sludge [gVSS], a quantity of methane gas formed per day [gCOD/gVSS/d]is computed according to a sequence similar to that according to thepresent invention as described hereinafter.

PROBLEMS TO BE SOLVED BY THE INVENTION

By the way, with the measuring apparatus as described above, gas phasereplacement is not taken into account in the measurement of specificmethanogenic activity as described above, and a long period of time isrequired for raising the anaerobic characteristics of the apparatus.Totally, 44 hours are required for sampling of the sludge, and duringthis period of time an operator is required to continuously monitor agauge without leaving the measuring apparatus, which is a heavy workload to the operator. In addition, measurement values are visually readby the operator from the scale, so that the read values may beinaccurate, and further careful operations are required to keep thenarrow-mouthed bottle without causing movement thereof. When measuringsludge with a low specific methanogenic activity, sometimes a NaOHaqueous solution may flow in the reverse direction from a gas holder tothe narrow-mouthed bottle with the specific methanogenic activitycomputed manually by the operator, which requires complicated operationsand makes it difficult to quickly compute the specific methanogenicactivity or to determine whether measured values on the specificmethanogenic activity are acceptable or not.

It is an object of the present invention to provide a specificmethanogenic activity measuring apparatus, which can solve the problemsin the conventional type of specific methanogenic activity measuringapparatus as described above, requires only a short period of time forraising the anaerobic characteristics, finishes all steps from samplingsludge up to measurement, and also which can automatically record aresult of measurement without requiring an operator to stay near themeasuring apparatus and continuously monitor the gauges, andresultantly, which does not give a large work load to the operator, norrequires the operator to pay minute attentions for statically keepingthe reaction vessel, and further, in which the NaOH solution never flowsin the reverse direction into the reaction vessel when measuring sludgewith low specific methanogenic activity, the operator is not required tomanually compute the specific methanogenic activity, the activity canquickly and easily be computed, and further determination can be made asto whether the measured specific methanogenic activity value isacceptable or not.

MEANS FOR SOLVING THE PROBLEMS

To achieve the objectives as described above, the invention provides aspecific methanogenic activity measuring apparatus having a measuringmeans for measuring specific methanogenic activity of sludge inanaerobic wastewater or soil processing and a recording means, and themeasuring apparatus has a pressure vessel with a cover removablyattached thereto, a carbon dioxide gas absorbing container, and athermostatic bath with the pressure vessel removable placed therein asthe measuring means, in which a pressure transducer based on thepressure-electricity converting system connected to the recorder isattached to the cover, a supporting member for the carbon dioxide gasabsorbing container is attached to an external bottom surface of thecarbon dioxide gas absorbing container, a gas piping for venturationpenetrating an internal surface of the container, and further a gaspiping with a valve for gas phase replacement to a cover of the pressurevessel respectively, and in the invention, a magnetic stirrer isattached to the internal bottom surface of the pressure vessel.

The inventions provide the advantages that the time required for raisingthe anaerobic characteristics of the apparatus is short, all steps fromsampling sludge up to final measurement can be finished within a shortperiod of time, also the apparatus itself can automatically record aresult of measurement, an operator is not required to stay near theapparatus for continuously monitoring the gauges, thus the work load ofthe operator is reduced, and further, an accurate result of measurementcan be obtained, minute attentions are not required for staticallykeeping the reaction vessel, and the NaOH solution never flows in thereverse direction into the reaction vessel when measuring sludge with alow specific methanogenic activity.

The invention also provides a screen display unit having a computingsection for automatically computing a quantity of methane formed per day[gCOD/gVSS/d] from information on pressure detected by a pressuretransducer based on a pressure-electricity converting system in themeasuring means as a recording means and a display section fordisplaying a computed value processed by the computing section; whereinthe computing section measures changes in pressure for a specifiedperiod of time for determination according to a pressure signal from thepressure transducer in the measuring means, converts the slope of thepressure change to a historical change in a quantity of formed gas andalso to a unit [gCOD/h] which can be expressed as a load correspondingto a methane gas forming rate per hour x[ml], computes a methane gasforming rate per day for one unit volume of sludge by dividing theconverted methane gas forming rate x[gCOD/h] by a total volume of sludge[gVSS] used for measurement; the computing section has an A/D convertorfor converting a pressure signal from the pressure transducer in themeasuring means to a digital signal, a determination time counter formanually setting a determination time therein and numerically displayinga determination time, a gVSS counter for manually setting a gVSS ofsludge therein and numerically displaying the gVSS of the sludge, and acontrol section for computing a methane forming rate [gCOD/gVSS/d] perday according to the pressure signal from the A/D converter, adetermination time from the determination time counter, and a gVSS ofthe sludge from the gVSS counter, or has, in place of the determinationtime counter and gVSS counter, a keyboard for entering a determinationtime and a gVSS for the sludge, a screen display unit for displaying onthe screen the determination time and the gVSS of the sludge enteredfrom the keyboard, a timer for counting a determination time inputtedfrom the keyboard, and a memory for storing therein a determination timeand a gVSS and enabling the control section to read and fetch datastored therein; and the display section comprises a plurality of lampsused for comparing a value of a methane forming rate [gCOD/gVSS/d]computed by the computing section to a threshold value and displaying aresult of comparison by turning ON or OFF discretely, and further, thedisplay section compares the value of methane forming rate [gCOD/gVSS/d]computed to the computing section to a criteria for determination anddisplays on the screen whether the result is acceptable or not.

In these inventions, a determining unit in the specific methanogenicactivity measuring apparatus automatically computes a methane formingrate per day [gCOD/gVSS/d] from information on pressure detected by apressure transducer based on the pressure-electricity converting systemin the measuring means, and displays the computed value. Namely,pressure change during a specified period of time for determination ismeasured according to a pressure signal from the pressure transducer,and the slope of the pressure change is converted to a historical changein the gas forming rate. Then the value is converted to a value [gCOD/h]which can be expressed as a load corresponding to a methane gas formingrate per hour x[ml]. This converted methane gas forming rate x[gCOD/h]is divided by a total quantity of sludge [gVSS] used for measurement toobtain a methane gas forming rate per day for one unit quantity ofsludge for computing a methane forming rate per day [gCOD/gVSS/d], sothat an operation is not required to manually compute a methane formingrate and the rate can quickly and easily be computed, and furtherwhether a measured methane forming rate is accepted or not can bedetermined.

DETAILED DESCRIPTION OF THE EMBODIMENTS

For better understanding of the present invention, detailed descriptionis made hereinafter for embodiments of the present invention withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional front view showing Embodiment 1 of thepresent invention;

FIG. 2 is a front view showing a longitudinal cross-section of a carbondioxide absorbing container according to Embodiment 1 ;

FIG. 3 is a flow chart showing operations of the carbon dioxideabsorbing container;

FIG. 4 is an explanatory view showing an initial state in an example ofa method of weighing sludge in Embodiment 1 ;

FIG. 5 is an explanatory view showing an intermediate state in theexample of weighing sludge;

FIG. 6 is an explanatory view showing a final state in the example ofweighing sludge;

FIG. 7 is a front view showing Embodiment 2 of the present invention;

FIG. 8 is a block diagram showing the configuration of an automaticdetermining means in Embodiment 2 ;

FIG. 9 is a view showing the appearance of the automatic determiningmeans;

FIG. 10 is a view showing a flow of operations of the automaticdetermining means;

FIG. 11 is a view showing the timing of operations of the automaticdetermining means;

FIG. 12 is a perspective view showing a specific methanogenic activitymeasuring apparatus based on the conventional technology but similar tothat according to the present invention; and

FIG. 13 is a view showing the flow of operations of the apparatus.

The specific methanogenic activity measuring apparatus according toEmbodiment 1 of the present invention shown in FIG. 1 and FIG. 2comprises a measuring means 1 and a recording means 2, and the measuringmeans 1 has a pressure vessel 4 with a cover 3 removably attachedthereto, a carbon dioxide absorbing container 6 removably accommodatedin the pressure vessel 4, and a thermostatic bath 7 with a stirrerremovably accommodated in the pressure vessel 4 with a pressuretransducer 8 based on the pressure-electricity system connected to therecording means 2 and gas pipings 11, 12 having a pair of valves for gasphase replacement 9, 10 coupled to the cover 3, and a magnetic stirrer13 is attached to an internal bottom surface of the pressure vessel 4.

A support piping 14 for supporting the carbon dioxide absorbingcontainer 6 is attached to an external bottom surface of the carbondioxide absorbing container 6, and gas piping 16 for ventilationpenetrating through a bottom surface thereof is provided at a centralportion of an internal bottom surface of the container. A magneticstirrer switch 17 for starting a driving unit for running the magneticstirrer 13 not shown in the figure is provided in the thermostatic waterbath 7.

With the measuring apparatus, an operating sequence when measuringspecific methanogenic activity of sludge is shown with passage of timein an operation flow chart in FIG. 3, and in this operating sequence,

(1) water is poured into the thermostatic water bath 7 of the measuringapparatus 1 by an operator with the temperature of the water in thethermostatic water bath 7 adjusted to 35° C. by turning the heatingswitch 18 ON;

(2) then the cover 3 for the pressure vessel 4 is removed, and aspecified quantity of sludge and a reaction mixture (50 ml of sludge and450 ml of reaction liquid, totally 500 ml) are poured into the vesselfor 1 minute;

(3) then the carbon dioxide absorbing container 6 is placed in thepressure vessel 4 with 20 ml of 20% sodium hydroxide solution filled inthe carbon dioxide absorbing container 6 filled in the carbon dioxidegas absorbing container 6 to remove CO₂, and then only methane gas is anobject for measurement (time 0);

(4) the cover 3 is set on the pressure vessel 4, the valves 9, 10 forgas phase replacement are opened to feed nitrogen gas from one of thegas piping 11 into the pressure vessel 4 to raise the anaerobiccharacteristics of the apparatus, and air is exhausted from the otherventilation piping 12 to replace the air in a hollow section of thepressure vessel 4 with nitrogen gas for around 0.5 minutes;

(5) then the two valves 9, 10 for gas phase replacement are closed, thepressure vessel is inserted into the water thermostatic water bath 7 athe temperature of 35° C. with the stirrer switch 17 turned ON to startoperation of the magnetic stirrer 13 and mix the sludge and reactionmixture within the pressure vessel 4, and the temperature within thepressure vessel 4 is stabilized within around 3 minutes;

(6) then the operator turns ON a switch of the recording means 2, inputspressure values detected during, for instance, 4 hours with the pressuretransducer 8 based on the pressure-electricity converting system intothe recorder 6, and terminates measurement, and

(7) thus specific methanogenic activity [gCOD/gVSS/d] is measured andcomputed by spending 24 hours as described in the example describedbelow to finish the entire operating sequence measurement, and in thiscase a time required for the entire sequence for measurement is around28 hours and 34 minutes

As described above, when measuring the specific methanogenic activity,information on the pressure detected by the pressure transducer 8, basedon the pressure electricity converting system provided between thepressure vessel 4 and recording unit 2, is inputted into the recordingmeans 2 for measurement, so that no work load is required for theoperator, and an excellent result of measurement can be obtained with awork load for an operator substantially reduced, and in addition,accurate information on measurement can be obtained.

EXAMPLE 1

Specific operating sequences in the “method of measuring a volume ofsludge” and “method of adjusting a reaction mixture” in step (2) abovein measurement of specific methanogenic activity of granular sludge asdescribed above is as follows.

Method of Measuring a Volume of Sludge

1) Anaerobic wastewater containing granular sludge is sampled from anupflow anaerobic sludge blanket tank (UASB tank), and is put in awide-mouthed beaker B with a capacity of 2L as shown in FIG. 4.

2) The anaerobic wastewater is poured into a filtering vessel S as shownin FIG. 5 to remove the wastewater and minute suspended materials tosome degree.

3) The granular sludge obtained through the sequence as described aboveis scooped with a dipper having a capacity of 50 ml to accurately obtainan dipper-full of sludge.

4) The granular sludge measured and obtained as described above is putin the pressure vessel 4 together with 450 ml of reaction mixtureadjusted as described below.

Method of Adjusting a Reaction Mixture

{circle around (1)} Constituent Solution of the Reaction Mixture

Solution A (buffer): A solution containing a buffer agent condensed to a100 times higher density as compared to that in ordinary use (pH=7.0),an indicator, vitamins, and rare metals.

Solution B (reductant): 2.5% sodium sulphate aqueous solution, which isused to adjust a reaction liquid into an anaerobic state.

Solution C (reductant): 2.5% stain chloric salt aqueous solution, whichis used to guide a reaction liquid into an aerobic state.

Solution D (reductant): 128/L sodium acetate aqueous solution (pH=7.0),10 ml of which is equivalent to 1 gCOD.

The reaction mixture is diluted and mixed with distilled water accordingto the following procedure for adjustment.

{circle around (2)} Adjustment Procedure

1) 5 ml of solution A is put with a pipet into an empty screw-mouthedbottle.

2) Accurately, 425 ml of service water is sampled with a 500 mlmesscylinder, and poured into t he screw-mouthed bottle.

3) Then, totally, 10 ml of solution D (by 5 ml twice) is poured into thethreaded-mouth bottle.

4) 5 ml of solution B is quickly poured with a pipet into thethreaded-mouth bottle.

5) Then 5 ml of solution C is quickly poured with a pipet into thebottle.

6) After the steps 4) and 5) above are finished, a cap for thethreaded-mouth bottle is tightly closed.

(Note 1): After the step 6, the color of the solution changes from blueto pink and then to transparent in association with reduction ofdissolved oxygen in the mixture.

(Note 2): A total time required for conditioning is in a range fromaround 15 to 30 minutes.

(Note 3): A total quantity of reaction mixture is 450 ml.

EXAMPLE 2

Computing Sequence

A sequence of computing specific methanogenic activity [gCOD/gVSS/d] inthe example above is as described below.

1) Pressure change for 4 hours from the start of measurement ismonitored.

2) Slope of the pressure change obtained as described above is computedto hourly change in a volume of formed methane gas:

 x=Dimensions of a capacity of the pressure vessel×y  (1)

wherein

x[ml/h]: Methane gas forming velocity, and

y[kgf/cm²/h]: Slope of pressure change

3) A volume x[ml] of methane formed per hour obtained as described aboveis converted to a unit [gCOD/h] which can be expressed as acorresponding load. In a case of methane, 1 [gCOD] corresponds to 350[ml].

4) A volume of methane formed per day for one unit volume of sludge iscomputed by dividing the volume of methane x[gCOD/h] described above bythe total volume of sludge [gVSS] used in the measurement.

5) Finally, a volume of methane formed per day [gCOD/gVSS/d] iscomputed.

Example of Computing

A practical case of computing a volume of formed methane according tothe above-described sequence is described below.

a) From the above-described computing sequence, it is understood thatspecific methanogenic activity (slope) when the measured pressure changefor 4 hours with the recording means 2 from start of measurement is 0.3[kgf/cm²], the specific methanogenic activity (slope) is computed asfollows:

0.3÷4=0.075[kgf/cm²/h]

b) Then, assuming that a capacity of the pressure vessel is 341 [cm³], avolume of formed gas is computed by converting the slope of pressurechange to hourly change in a volume of formed gas according to theequation (1) in the computing step 2) as follows:

Volume of formed gasx=341×0.0756, namelyx=25.58[ml/h]

c) Herein, by converting the volume x[ml] for methane gas formed perhour to the unit [gCOD/h] expressing a corresponding load according tothe step 3) above, the specific methanogenic activity (slope) iscomputed as follows:

25.28÷350=0.073[gCOD/h]

d) Then, assuming that the total volume of sludge used in measurement is4.22 [gVSS], a volume of methane formed per day for one unit volume ofsludge is computed according to the step 4) above as follows:

0.073÷4.22=0.0173[gCOD/gVSS/h]

e) Then, a volume of methane formed per day [gCOD/gVSS/d] is computedaccording to the step 4) above as follows:

0.0173×24=0.415[gCOD/gVSS/d]

This is a value indicating the specific methanogenic activity to beobtained.

Embodiment 2 of the present invention showing in FIG. 7 to FIG. 9 isdifferent from Embodiment 1 in that an automatic determining unit 20 isprovided in place of the recording means in Embodiment 1 , and a heatingswitch 18 is provided in the measuring means 1. This automaticdetermining means 20 has a basic body 12 of the determining unit, andthis basic body 21 comprises an amplifier 22 for amplifying a pressuresignal outputted from the pressure transducer 8 as shown in FIG. 8, anA/D converter 23 for converting the amplified pressure signal from thisamplifier 22 to a digital signal, and a control section 26 forcontrolling each component and especially providing controls forautomatic measurement of specific methanogenic activity. The controlsection 26 provides controls for computing a volume of methane formedper day [gCOD/gVSS/d] according to data on determination time and a gVSSof sludge provided from the gVSS counter.

Further, the basic body 21 of the measuring means comprises a D/Aconverter 27 for converting data from the control section 26 to ananalog signal and sending the analog signal to the recorder 5, adetermination time counter 33 for manually setting determination time inthe control section 26, counting the determination time and numericallydisplaying the determination time, and a gVSS counter 34 for manuallysetting a gVSS volume of sludge in the control section 26 andnumerically displaying the gVSS volume of sludge.

Further, the main body 21 of the measuring means comprises a DPM 43 fordisplaying such data as specific methanogenic activity obtained asdescribed above (corresponding to a digital panel meter, a digitaldisplay unit, or a screen display unit as claimed herein), five piecesof lamps 30 a to 30 e each lighting up for indicating contents ofdetermination for specific methanogenic activity value, five pieces oflimps 40 a to 40 e lighting up for indicating contents of determinationon a specific methanogenic activity value step by step, a power switch32 for turning ON/OFF the power 31, and a power supply section 45 forsupplying a DC current to each section of the basic body 21 of thedetermining means. It should be noted that other various types ofinstruction switch are provided but are not shown herein. Theinstruction switches include a switch for instructing a lamp test or areset switch for instructing completion of measurement and start of thetest measurement.

The lamps 30 a to 30 e indicate operational states as shown in FIG. 9,and comprise the power lamp 30 a lighting up when power is turned ON, afailure indicating lamp 30 b lighting up for indicating a failure, anin-measurement indicating lamp 30 lighting up for indicating thatmeasurement is being executed (the basic body 21 of the determiningmeans is operating), a measurement completion indicating lamp 30 dlighting up for indicating that measurement has been finished, and alamp test indicating lamp 30 e lighting up for indicating whether eachlamp is working normally or not.

The lamps 40 a to 40 e indicate a result of comparison of a measuredspecific methanogenic activity value to a criteria for determinationpreviously set in the control section 26 in five stages. The 5-stageindicator lamps consist of the HH-display lamp 40 a lighting up anddisplaying “HH: Quite excellent”, MH-display lamp 40 b lighting up anddisplaying “MH: Relatively better” ML-display lamp 40 c lighting up anddisplaying “ML: Relatively worse”, L-display lamp 40 d lighting anddisplaying “L: Not good”, and LL-display lamp 40 e lighting up andindicating “LL: Extremely bad”.

In the figure, the determination time counter 33 and gVSS counter 34 arethose turned for setting on the panel, but other configuration isallowable. For instance, the configuration is allowable in which thereare provided a keyboard for entering determination time and a gVSS rateof sludge, a screen display unit for displaying the determination timeand gVSS rate of sludge entered from the keyboard on the screen, a timerfor counting the determination time entered from the keyboard, and amemory for storing therein the determination time and gVSS of sludgefrom which the control section reads out and fetches the stored data.

Next description is made at first for general operations of the basicbody 21 of the determining means having the configuration as describedabove, and then for a sequence of operations for measuring specificmethanogenic activity of granular sludge.

When the power switch 32 is turned ON, power is supplied from the powersupply section 45 to the basic body 21 of the determining means, andautomatic measurement of specific methanogenic activity of the granularsludge is started. A pressure signal from the pressure transducer 8 isamplified by the amplifier 22, and this amplified pressure signal isconverted to a digital signal by the A/D converter 23 and the digitalsignal is sent to the control section 26. Determination time is set inthe control section 26 by manually operating the determination counter33 for counting the determination time and also numerically displayingthe determination time. Also a specified gVSS of sludge is set in thecontrol section 26 by manually operating the gVSS counter 34, and thegVSS of sludge is numerically displayed. According to the determinationtime and gVSS of sludge set by manually operating the determination timecounter 33 and gVSS counter 34 as described above, the control section26 provides controls for computing the specific methanogenic activity[gVOD/gVSS/d] according to a flow and timing of operations as shown inFIG. 6 and FIG. 7.

The specific methanogenic activity value [gCOD/gVSS/d] computed asdescribed above is converted by the D/A converter 27 to an analog signaland the analog signal is sent to the recorder 5, where the measuredvalue is recorded with such a tool as a pen on recording paper. Also thecontrol section 26 provides controls for discretely lighting up each ofthe lamps 30 (power lamp 30 a, failure displaying lamp 30 b,in-measurement display lamp 30 c, measurement-completion indicator lamp30 d, and lamp test indicator lamp 30 e) in response to an operatingstate as described detailedly in relation to a sequence of operationsfor measuring specific methanogenic activity of sludge as describedhereinafter. Further, the control section 26 provides controls fordisplaying a measured specific methanogenic activity value with the DPM43 as well as for lighting up the lamps 40 (HH-display lamp 40 a,MH-display lamp 40 b, ML-display lamp 40 c, L-display lamp 40 d, andLL-display lamp 40 e) for displaying contents of the measurement in fivestages as detailedly described in the sequence of operations formeasuring specific methanogenic activity of sludge hereinafter.

Description is made hereinafter for a sequence of operations formeasuring specific methanogenic activity of sludge with the measuringdevice as described above with reference to an operation flow chart inFIG. 10.

(A) An operator pours water into the thermostatic water bath 7 of themeasuring means 1, and turns ON the heating switch 18 to set thetemperature of the water in the thermostatic water bath 7 to 35° C.;

(B) then the operator removes the cover 3 for the pressure vessel 4 andpours a specified volume of sludge and a specified quantity of reactionmixture (50 ml of sludge and 450 ml of reaction mixture, totally 500 ml)in the pressure vessel 4 spending 1 hour;

(C) then the operator places the carbon dioxide absorbing vessel 6 inthe pressure vessel 4 and fills 200 ml of 20% sodium hydroxide aqueoussolution in the carbon dioxide absorbing vessel 6 to remove CO₂ so thatonly methane gas is measured (time 0),

(D) then the operator sets the cover 3 on the pressure vessel 4, opensthe valves 9, 10 for gas phase replacement to raise the anaerobiccharacteristics of the apparatus, and further feeds nitrogen gas fromone of the aeration pipes 11 into the pressure vessel 4 and at the sametime exhausts the gas from the other gas pipe 12 to replace air withinan internal capacity of the pressure vessel 4 with the nitrogen gas byspending around 10 minutes; and

(E) Then the operator closes the valves 9, 10 for gas phase replacement,immerses the pressure vessel 4 into the thermostatic water bath 7 havingthe temperature of 35° C., turns ON the stirrer switch 17 to start themagnetic stirrer 13 and mix sludge and reaction mixture within thepressure vessel, and with the operations described above, in around 10minutes, inside of the pressure vessel 4 is thermally stabilized, andpress-in information (0 to 5 kgf/cm²) is outputted from the pressuretransducer 8 as shown in FIG. 8(a).

(F) In this step, the operator turns ON the power switch 32 with thepower lamp 30 a lit up.

(G) Then the operator operates the determination time counter 33 to setdetermination time (4 hours) in the control section 26 as shown in FIG.11(b) and the time is displayed on the determination time counter 33.

(H) Then the operator operates the gVSS counter 34 to input a gVSS ofsludge, and the rate is displayed on the gVSS counter 34.

(J) When the operator lights up on the in-measurement lamp 30 c, thestirrer switch 17 is turned ON with a mixing operation of the magneticstirrer 13 started, and an operation of the recorder 5 for recording isstarted as shown in FIG. 11(h) under controls by the control section 26.

(K) When there comes the determination time, operations of thedetermination time counter are finished, and the specific methanogenicactivity value X₁ computed through the equation (1) under control by thecontrol section 26 as shown in FIG. 11(d) is displayed on the DPM 43.$\begin{matrix}{X_{1} = \frac{\Delta \quad P_{2} \times V \times T_{2}}{\left( {T_{1} - T_{4}} \right) \times {gCOD} \times {gVSS}}} & (1)\end{matrix}$

In this equation (1), ΔP₂ indicates a pre sure changed from a point oftime when the computing-ignorable time has passed until thedetermination time, V indicates an internal capacity of the pressurevessel, T₂ indicates a determination time per day (24 hours), T₁indicates actual determination time (4 hours), T₄ indicates acomputing-ignorable time (1 hour), gCOD indicates specific methanogenicactivity (slope), and gVSS indicates a volume of sludge.

(L) As shown in FIG. 11(i), determination is made as to whether themeasured specific methanogenic activity value is acceptable or notaccording to the specific methanogenic activity value X₁ displayed onthe DPM 43 as well as to a criteria for determination previously set inthe control section 26, and then any of display values HH (High High,Quite excellent), MH (Middle High: Relatively better), ML (Middle Low:Relatively worse, L (Low: Not good), and LL (Low Low: Extremely bad) isdisplayed on a corresponding one of the determination lamps 40 (40 a, 40b, 40 c, and 40 d).

(M) Then as described above, the specific methanogenic activity value X₁computed through the equation (1) is recorded once for every 12 minutesin the recorder 5 under controls by the control section 26 with themagnetic stirrer 19 started, and when the specific methanogenic activityvalue X₁ of 01 or below are recorded two times successively, thein-measurement lamp 30 c is turned out with the completion lamp 30 d litup as shown in FIG. 11(k), and also the stirrer switch 17 is turned OFFwith mixing operations of the magnetic stirrer 13 stopped.

(N) When the operator turns OFF the power switch 32, the completion lamp30 d turns out with a displayed value on the DPM 43 cleared, and thenthe initial state is restored with measurement terminated.

(O) In this measurement, for instance one hour is set as acomputing-ignorable time (T₄) as shown in FIG. 11(j). Also it is assumedherein that, as shown in FIG. 11(c), computing time (T₃) by the controlsection 26 is executed at a time interval of 0.2 hour (12 minutes).

What is claimed is:
 1. A specific methanogenic activity measuringapparatus comprising a measuring means for measuring specificmethanogenic activity of sludge or soil during aerobic wastewatertreatment and a recording means, the measuring means comprising athermostatic water bath, a pressure vessel removably accommodated in thewater bath, a cover removably placed on the pressure vessel for sealingan open compartment formed therein, a carbon dioxide absorbing containerremovably disposed in the open compartment, a supporting member attachedto the carbon dioxide absorbing container and extending to a bottom wallof the open compartment for supporting said carbon dioxide absorbingcontainer in the open compartment, a pressure transducer attached to thecover for converting a detected pressure into an electrical signal andtransmitting the electrical signal to the recording means, ventilationmeans comprising piping extending through a central portion of thecarbon dioxide absorbing container, and gas replacement means attachedto the cover and comprising an inlet line having a valve disposedtherein for introducing a purge gas into the pressure vessel and anoutlet line having a valve disposed therein for exhausting air from thepressure vessel.
 2. The specific methanogenic activity measuringapparatus according to claim 1, wherein a magnetic stirrer is attachedto an internal bottom surface of the pressure vessel.
 3. The specificmethanogenic activity measuring apparatus according to claim 1, whereinthe recording means comprises a computing section for automaticallycomputing a specific methanogenic activity, gCOD/gVSS/d, frominformation on the pressure detected by the pressure transducer and adisplay section for displaying a value computed in the computingsection.
 4. The specific methanogenic activity measuring apparatusaccording to claim 3, wherein the computing section measures a change ofpressure at a specified determination time according to a pressuresignal from the pressure transducer in the measuring means and convertsslope in pressure change to hourly change of gas forming rate and alsoto a unit, gCOD/h, which can be expressed as a load corresponding to thehourly methane gas forming rate xml, and further divides the computedmethane gas forming rate xgCOD/h by a total volume of sludge used forthe measurement to obtain a methane gas volume per day for one unit ofsludge to obtain a volume of methane gas formed per day, gCOD/gVSS/d. 5.A specific methanogenic activity measuring apparatus according to claim3, wherein the computing section comprises an A/D converter forconverting a pressure signal from the pressure transducer in themeasuring means to a digital signal, a determination time counter formanually setting a determination time, counting the determination timeand numerically displaying the determination time, a gVSS counter formanually setting a gVSS of sludge and numerically displaying the gVSS ofsludge thereon, and a control section for providing controls forcomputing a specific methanogenic activity, gCOD/gVSS/d, to a pressuresignal from the A/D converter as well as to the determination time fromthe determination counter and the gVSS of sludge from the gVSS counter.6. The specific methanogenic activity measuring apparatus according toclaim 5, wherein the functions of the determination time counter andgVSS counter are provided by, a keyboard for entering a determinationtime and a gVSS of sludge, a screen display unit for displaying thedetermination time and gVSS of sludge entered from the keyboard on thescreen thereof, a timer for counting the determination-time entered fromthe keyboard, and a memory for storing therein the determination timeand gVSS of sludge and enabling the control section to read and fetchthe stored data therefrom.
 7. The specific methanogenic activitymeasuring apparatus according to claim 3, wherein the display sectioncomprises a plurality of lamps which light up for indicating a result ofa comparison of a value for specific methanogenic activity, gCOD/gVSS/d,computed by the computing section to a criteria for determination instages.
 8. The specific methanogenic activity measuring apparatusaccording to claim 3, wherein the display section is a screen displayunit for displaying a result of a comparison of a value for the specificmethanogenic activity, gCOD/gVSS/d, computed by the outputting sectionto a criteria for determination on a screen thereof.